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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 18 October 2011 by dana1981

At this point in the Lessons from Past Climate Predictions series, we're running out of global temperature predictions to evaluate, so now may be a good time to summarize what we've seen thus far. So let's just get right to the good stuff:

As you can see in Figure 1, the more mainstream climate science predictions (generally the warmer colors) have mostly done well (Kellogg in 1979 being the main exception), and the "skeptics" (generally cooler colors) have generally done rather poorly, universally predicting less warming than has been observed.

Note that for simplicity and clarity, the figures in this post only include the best estimate predictions/projections of each paper we examined, although some included uncertainty ranges, and others didn't. For details regarding each prediction, see the individual posts in the 'Lessons' series.

Figure 1 is a bit cluttered, but we can parse the predictions out by isolating the "skeptic" and mainstream predictions.

"Skeptic" Predictions

Figure 2: As in Figure 1, but just the "skeptic" predictions.

There are a few interesting things to note from these figures. For example, we were unable to identify any "skeptic" or global cooling predictions prior to 2000 (note that the few so-called "1970s global cooling predictions" were based on aerosol emissions scenarios which did not occur, and thus are not worth evaluating). The lone exception in Figure 2 is Lindzen's, which we reconstructed from comments he made in a 1989 MIT Tech Talk, but which is not a prediction he made himself.

Those few "skeptics" who have made predictions have not fared well thus far. McLean's prediction that 2011 would return to 1956-level temperatures sticks out in particular - we will do a post updating the status of his prediction in the near future. Akasofu, who predicted 0.5°C global surface temperature warming between 2000 and 2100, has thus far been the closest amongst the "skeptics". However, his prediction completely ignores the warming due to the increased greenhouse effect, and in general fails to examine the causes of the temperature changes that he models and predicts.

Mainstream Predictions

Figure 3: As in Figure 1, but just the mainstream climate science predictions.

The global warming predictions made by mainstream climate scientists have all fared reasonably well, with the exception of Kellogg's in 1979, whose linear nature we found puzzling. Hansen's 1988 prediction (we show his Scenario B with the observed greenhouse gas changes taken into account, as described in the Hansen Lessons post) has been somewhat high, mainly because the equilibrium climate sensitivity in the model he used was 4.2°C for doubled CO2, which is higher than today's best estimate of 3°C. Overall, the IPCC projections have thus far been the most accurate.

It's also interesting to specifically examine the projections which applied their models to most or all of the instrumental temperature record (Figure 4).

The difference between the two models in Figure 4 is that Broecker attempted to incorporate 'natural cycles' (which he called 'Camp Century cycles', based on Greenland ice core records), whereas the IPCC TAR model only includes anthropogenic effects. The IPCC TAR model-data comparison clearly shows that human effects had relatively little influence over the early-20th Century warming, but dominated the temperature change since the mid-20th Century.

What's in Store?

Since the IPCC projections have thus far been the most accurate, it's worthwhile to see what we have in store if their accuracy continues. Currently we're on track with the SRES A2 emissions path, so we can consider this the 'business-as-usual' scenario.

Skeptical Science contributor jg has done a great job putting each of the predictions and the combinations above into an animated GIF, finishing off with the AR4 future projections for Scenarios A2 and B1 (Figure 5). Scenario B1 involves taking serious action to reduce greenhouse gas emissions.

If we continue on a business-as-usual path, the IPCC AR4 projects that we are most likely on track for 4°C warming above pre-industrial levels by 2100. We will surpass the 'danger limit' of 2°C warming above pre-industrial levels by the mid-21st Century. Even in Scenario B1 we pass the danger limit, but by a much smaller margin. This is pretty strong evidence that we need to take action very soon to steer away from our current business-as-usual emissions path.

Comments

While I like the visibility of how wrong the "skeptic" predictions have been, it would be nice to see the mainstream model predictions start at the point from when they were published instead of how far back they reach in hindcast. So the first IPCC assessment's models should start at 1990, the second in 1996, etc.

Dana, you could make your hypothetical version of Lindzen's predictions look even worse if you moved them down another arbitrary 0.25C or so.

Or you could use the same baseline adjustment method you used for the other lines, in which case is would be relatively close to the observed temperatures.

It's really a moot point, though, since you are the one that generated the data you claim to be Lindzen's prediction.

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Response:

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It would be great if so called skeptics would actually read and follow links for more detailed explanations (the relevant link is provided in the post above), rather than simply looking at the pretty pictures and jumping to unfounded conclusions (which seems to be pretty much how the skeptical mind consistently works on the subject of climate change -- it's oh so much easier to see what you want to see than to learn and consider the facts).

Lindzen's proposal results in ridiculously inaccurate temperature predictions, even back to 1958, because that's how ridiculous his position is. A climate sensitivity as low as his requires that the climate be more stable than has been demonstrated in this entire century, let alone the last 30 years of AGW.

Indeed, comments policy "No accusations of deception". CharlieA has done this before and is doing it again now.

The origin of the offset is clear if one actually invests the time to read the relevant post, something CharlieA has apparently not done.

Lindzen has not gone the trouble to make his own projection/s. He loves to berate his colleagues and their efforts to predict what the future holds for a doubling of CO2, but he is either incapable or not willing to make his own predictions. So one has to make a best estimate based on what information Lindzen has volunteered in terms of climate sensitivity and expected temperature change.

If one does that, one obtains very little warming for doubling CO2 because Lindzen believes (or has convinced himself) that climate sensitivity is unrealistically low. The huge problem for Lindzen (and his supporters) is that his own arguments have been contradicted by observations-- in fact, his bold proclamation made at MIT in 1989 was wrong the moment he said it.

Now if Charlie A has a problem with what Dana did and wants to try and defend Lindzen's refuted claims, then he (and others) can argue that on the relevant thread (link provided by KR), but without suggesting deception. But CharlieA should note the bolded caveats provided by Dana.

This post very nicely demonstrates who has had the better track record when making predictions about global temperatures, and it is not the "skeptics" and those in denial about AGW.

There were several comments made by Lindzen which went into the reconstruction of what his temperature prediction might have looked like, as explained in the linked post in question.

"The trouble is that the earlier data suggest that one is starting at what probably was an anomalous minimum near 1880. The entire record would more likely be saying that the rise is 0.1 degree plus or minus 0.3 degree....I would say, and I don't think I'm going out on a very big limb, that the data as we have it does not support a warming. Whether it contradicts it is a matter of taste...I personally feel that the likelihood over the next century of greenhouse warming reaching magnitudes comparable to natural variability seems small"

In other words, Lindzen was both saying that the surface temperature had hardly warmed (~0.1°C) from 1880 to 1989, and that it would continue to hardly warm (~0.1°C) over the next century. The Lindzen reconstruction reflects both components.

Dana1981, please explain why Lindzen's 1989 prediction (as interpreted and generated by you) differs from measured global temperature anomaly by about 0.5C, even in the start year of the prediction.

If you used the same technique to baseline(offset) your "Lindzen" data in the same way you adjusted the baselines of the IPCC projections, what would your hypothetical 1989 Lindzen prediction be in 1989?

Lindzen effectively predicted 0.01°C warming per decade, so if we ignore half of his incorrect comments (claiming 0.1°C warming from 1880 to 1989), he would have predicted about 0.02°C warming from 1989 to 2011, whereas GISTEMP observed about 0.4°C warming over that period. So Lindzen's would still be off by 0.38°C (in the ballpark of Easterbrook A).

@#9 Dana -- you did not address the difference in how you offset the baseline for the various projections. It appears that you used a baseline of 1880 for your interpretation of Lindzen's prediction. Correct?

It also appears that you have offset the IPCC projections to match more recently observed data. Correct?

What would the Lindzen plot look like if you offset that data using the same adjustment procedure you used for the IPCC projection?

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Response:

[dana1981] I answered the question in comment #9. It would be off by 0.38°C in 2010.

Unfortunately I'm not up to the task of adjusting these projections according to how emissions have actually panned out in the last 30 years, but it seems to me that Hansen did pretty well even that long ago.